To determine the cytochrome P450 (CYP) primarily expressed after styrene exposure, seven forms of hepatic CYP mRNA in rats treated with 600 mg kg(-1) styrene were examined. CYP1A2, CYP2B1/2, CYP2E1 and CYP3A2 mRNA were observed using real-time LightCycler PCR. The amount of CYP2B1 mRNA was significantly increased, 47-fold compared with controls, suggesting that this CYP is the primary cytochrome P450 in rats exposed to styrene. Significant increases in the amount of CYP2E1, CYP1A2 and CYP2B2 mRNA were also observed after styrene exposure, and their increase levels were 3.1-, 1.7- and 1.7-fold higher than controls, respectively. Western blot analysis also indicated that the protein levels of CYP2B1, CYP2B2, CYP2E1 and CYP1A2 showed clear increases after styrene treatment, corresponding to their mRNA expression. CYP2C11 mRNA decreased significantly in rats after styrene exposure. CYP1A1 was detected at the mRNA level in rat liver, but it was not detected at the protein level. The expression of epoxide hydrolase (EH), involved in Phase I drug metabolism, was also examined. EH mRNA increased 2-fold compared with controls after styrene exposure. Styrene thus appears to be a chemical compound that induces multiple CYPs. The results demonstrate that CYP2B1 is the primarily induced CYP form by styrene treatment to rats at acute toxic level.